AAg 2M[VO 4] 2 with A=Sr2 + or Ba2 + present a series of layered compounds featuring a triangular lattice of transition metal cations, M = Co2 + or Ni2 +, connected via nonmagnetic ortho-vanadates, which provide the magnetic superexchange within the layers. For this series of insulating compounds, ferromagnetic long-range order below 10 K is suggested by magnetization and specific heat measurements and confirmed by neutron diffraction experiments. We have investigated the impact of the spacer size of A2 + separating the layers leading to a tilting of the vanadates and consequently inducing a change in the effective magnetic correlations. Magnetization and specific heat measurements corroborate the important dependence of the magnetic superexchange on the orientation of the vanadates and the respective spin system. Furthermore, the ground state properties of the spin systems, S=1 (Ni2 +) and S=3/2 (Co2 +) in their respective octahedral coordination of oxygen, are evaluated. Calculated magnetic moments of the single ion complexes agree well with the magnetic structure. We, furthermore, report the dependence of T c on applied isotropic pressure suggestive of a pressure effect on the effective ferromagnetic exchange coupling constants. In addition spectroscopic investigations probing the electronic structure of the [MO 6] complexes and the vibrational structure of the [VO 4] units are given.
|期刊||Physical Review B - Condensed Matter and Materials Physics|
|出版狀態||Published - 2012 6月 20|
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